Let A and B be disjoint, the complement of A is everything not in A and the complement of B is everything not in B. The union of the two is therefore everything that is not in A or everything that is not in B, so it must be the entire universe.
The answers is 3/9 which you can check by reducing. It reduces to 1/3. Basically you go 1/3 = x/9 then cross multiple to get 9=3x do the division so 3x/3 and 9/3 and you get 3/9.
